A magnetoresistive random access memory (MRAM) is known as a type of semiconductor memory device. The MRAM is a memory device that uses a magnetoresistive element, having a magnetoresistive effect, as a memory cell which stores information. Writing methods for MRAMs include a spin-transfer torque writing method. The spin-transfer torque writing method is advantageous in high integration, low power consumption, and high performance, due to the characteristic that the smaller the size of a magnetic body, the smaller the spin-transfer torque current necessary for magnetization inversion.
The magnetoresistive element stores binary data in accordance with a magnetization direction of a storage layer. Therefore, to realize a high-performance MRAM, it is important to improve data storage characteristics of the storage layer.